JP2009-204086A discloses a load sensing valve device including a plurality of main valves and a plurality of compensator valves associated with each respective main valve.
The compensator valve is disposed in such a manner that an axis line thereof is at right angles to a spool of the main valve (hereinafter, called main spool).
The compensator valve disposes a variable throttle portion (hereinafter, called compensator throttle portion) in a passage course which is downstream of the main valve and which connects the main valve with an actuator port.
Moreover, a spool of the compensator valve (hereinafter, called compensator spool) has one end thereof facing a first pressure chamber and the other end thereof facing a second pressure chamber.
Furthermore, pressure of the upstream side of the compensator throttle portion is introduced into the first pressure chamber, and a maximum load pressure of actuators connected to the plurality of main valves is introduced into the second pressure chamber.
The compensator valve controls an opening of the compensator throttle portion in accordance with the pressures of the first pilot chamber and the second pilot chamber, and maintains a constant flow dividing ratio according to the openings of the main valves regardless of the variation in load pressure of the plurality of actuators.
Moreover, a selector valve is incorporated into the compensator spool. One end of the selector valve faces a maximum load pressure introduction chamber communicating with the second pressure chamber, and the other end thereof faces a load pressure introduction chamber formed in the compensator spool.
The load pressure introduction chamber communicates with an actuator port of the main valve with which the compensator valve is associated, via an introduction port formed in the compensator spool. However, the area of the opening of the introduction port is substantially constant, regardless of the moved position of the compensator spool.
The selector valve is configured to guide the pressure of the load pressure introduction chamber to the maximum load pressure introduction chamber, when the load pressure guided to the load pressure introduction chamber is higher than the pressure of the maximum load pressure introduction chamber.
Thereafter, a regulator of a pump operates in accordance with the maximum load pressure guided into the maximum load pressure introduction chamber, and a tilt angle of a variable displacement pump is controlled.